This invention pertains to an apparatus for transferring toner from a magnetic image-storage medium to paper or other toner-adherable receiving medium. Specifically, it pertains to such an apparatus in which the magnetic image-storage medium is carried on a resilient backing and mounted slidably therewith to allow for slip action between the two when a pressure roller presses paper against the magnetic medium during toner transfer.
The present invention is particularly suited to be used in a magnetographic reproduction system having a magnetic image-storage medium on which an electromagnetic read/write head produces magnetic images. The image-containing medium is transported past a toner decorator having a supply of toner and means for presenting the toner to the medium. The magnetic images in the medium attract the toner, thereby creating toner images on the medium. According to a preferred embodiment, the medium, and thereby the toner images, is then bombarded with positive ions from a corona discharge device. A toner-adherable receiving medium such as paper is then fed into the system after it has first been given a positive charge. This prevents the toner from not prematurely jumping from the medium to the paper. The paper is then fed adjacent the image-storage medium to a toner transfer apparatus made according to this invention. At this point, the paper is also provided with a charging field which acts to draw the positively-charged toner off of the medium and onto the paper. The toner is finally fused to the paper in a downstream heat and/or pressure fusing operation. After toner transfer, the image-storage medium is cleaned and erased in preparation for a repeat of the cycle just described with new images.
Directing attention directly to the toner transfer apparatus of this invention, it has been discovered that the magnetic image-storage medium, although manufactured to be a smooth surface, in fact has an uneven surface due to dust and other surface-laden pollutants which end up on the magnetic-image-storage medium surface. Further, it has been found that if too much pressure is used during the transfer process, "ghosts" are impressed on the magnetic medium. These cause further problems with subsequent magnetic imaging and toner transferring.
Also, the magnetic medium normally is disposed on a drum core which has a relatively large radius as compared to the pressure roller used to press the paper against the medium during transfer. It is a characteristic of the paper to break away most easily from the roller since it has a smaller diameter and places a greater stress on the paper.
Finally, a significant disadvantage of conventional roller transfer systems is that the magnetic medium is attached to the drum core on which it is mounted in a substantially fixed position. When paper is pressed against the medium, it is stressed as it responds to the various forces applied to it along its travel path. One result of this is that there typically is movement between the magnetic medium and the paper due to differences in path lengths traveled by the medium and the paper in the region of contact.
It is therefore a general object of the present invention to provide a system having improved toner transfer characteristics.
More specifically, it is an object to provide such an apparatus in which controlled, limited pressure is applied to the magnetic medium during the transfer process.
It is also an object to provide an apparatus in which the paper and magnetic medium are maintained substantially stationary relative to each other during the toner transfer process.
Thus, it is specifically an object of the present invention to provide an apparatus in which the magnetic medium is slidably disposed on a resilient backing.
It is a further object to provide a toner transfer apparatus having a toner-image carrying drum and a pressure roller which creates a buckle in the magnetic medium downstream of the pressured contact region with the paper during toner transfer to enhance the separation of paper and magnetic medium at the completion of the toner transfer process.
My present invention satisfies these and other objects by providing a magnetic image-storage medium which is mounted preferably on a resilient backing on a support which allows the magnetic medium to freely slide along a path along which the medium is transported. A pressure roller, optionally having a resilient surface layer, is placable against paper which is transported between the roller and the magnetic medium. The paper is in turn pressed against the magnetic medium, thereby distorting the underlying backing layer.
The deformation in the magnetic medium resulting from the pressured contact with the roller produces a slip action between the magnetic medium and the backing. The resulting reduction in path length is accommodated by a buckling in the medium downstream in the travel path adjacent the pressured contact region. There is thus developed a limited pressure contact region for toner transfer coupled with slip action between the magnetic medium and its associated backing. This results in substantially reduced relative motion between the toner-receiving paper and the magnetic medium during toner transfer. Additionally, the buckling effect creates a small-radius bend in the magnetic medium which is less than the circumferential radius of the pressure roller, thereby enhancing separation of the paper from the magnetic medium. These and additional objects and advantages of the present invention will be more clearly understood from a consideration of the drawings and the following detailed description of the preferred embodiment.